The present invention relates to rotors generally and, more particularly, but not by way of limitation to a novel injection molded threaded rotor for linear actuator.
One type of linear actuator is constructed by providing a threaded rotor inside an electric motor A complementarily threaded leadscrew is inserted through the rotor and rotor rotation causes the leadscrew to selectively advance linearly in one direction or the other depending on the direction of rotation of the rotor. One family of electric motors used in such applications is the step motor or more specifically, the hybrid step motor.
The traditional method of manufacturing a threaded rotor is to machine the threaded rotor portion of the motor from a bearing type material, such as bronze. This is a very labor intensive and costly operation for a number of reasons, among which are:
(1) Raw material is generally costly and there is a substantial amount of waste.
(2) Often, the thread form used is an acme thread and proper machining of the threads requires several operations.
(3) Materials that are good bearing materials do not necessarily machine easily, a good example being bronze.
In addition the process of machining these components produces parts that do not perform efficiently due to the generally poor surface finish of cut threads.
In other applications, it is common to use a thermoplastic material for the rotor, the thermoplastic material incorporating solid lubricants such as PTFE or silicone for increased efficiency Often, these parts use threads that are formed by injection molding This creates a more efficient thread form, due to the better surface finish Unfortunately the extension(s) of the threaded portion that create one or more bearing surfaces are not stable when formed of thermoplastic.
Consequently, it would be desirable to have a compound rotor that had the favorable characteristics of a thermoplastic threaded rotor, such as low coefficient of friction of the thermoplastic, with the stability of metal in the critical bearing journal area(s).
Accordingly, it is a principal object of the present invention to provide a compound rotor for a linear actuator that has an injection molded thermoplastic threaded portion, but with one or more bearing journal areas formed of metal.
It is a further object of the invention to provide such a compound rotor that can be easily and economically manufactured
It is another object of the invention to provide such a compound rotor that can be produced in part, in an unscrewing mold.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.
The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a threaded rotor for a linear actuator, comprising a generally cylindrical, metallic shell/insert; and a generally cylindrical threaded thermoplastic member disposed in a wall of said generally cylindrical shell/insert, said threaded thermoplastic member having threads formed on an inner surface thereof and engagable with complementary threads formed on an outer surface of a shaft to be inserted in said generally cylindrical shell/insert.